It has been proposed to provide seat belts and also air-bags for use in a motor vehicles to restrain seat occupants during an accident situation. It is known that, for the front seat occupants in a vehicle, if the seat belt and/or air-bag can prevent an occupant from reaching the dashboard or steering wheel in front of the seat during an accident, then the risk of injury to the seat occupant may be minimised.
In any accident situation, the energy that has to be absorbed by the seat belt and/or air-bag to prevent a seat occupant from reaching the dashboard depends upon a number of different factors, including the severity of the accident or, in other words, the degree of deceleration experienced by the vehicle, and also the weight of the seat occupant. It is clear that more energy has to be absorbed by a heavy person than if the seat is occupied by a light person in a particular accident situation. Also, more energy has to be absorbed in a severe high speed accident than in a low speed accident.
It has been proposed to utilise a force limiter associated with a seat belt for a seat occupant, the force limiter having an adjustable force level so that the energy absorbed by the force limiter may be adjusted. For example, the force limiter may have a force level or energy absorption level that can be changed from a high level to a lower level at a designated time period after commencement of an accident situation, or which can be changed in response to a signal indicative of the severity of a particular accident.
It is to be understood that, generally speaking, a heavy person may be capable of withstanding a much higher energy absorption level than a light person. However, it is always desirable to keep the energy absorption level applied to any seat occupant as low as possible. If a high energy absorption level is necessary, then that high energy absorption level should be used for as short a time as possible.
It has been proposed to control the energy absorption level of a seat belt force limiter by using weight sensors which determine the weight of a seat occupant, the weight sensors providing signals to a control unit, with the control unit then selectively adjusting the energy absorption level of the force limiter. The control unit may control the energy absorption level not only in dependence upon the weight of the seat occupant, but also in dependence upon the severity of the accident. However, such a sophisticated control arrangement is very expensive to implement.
The present invention seeks to provide an improved safety device.
According to this invention there is provided a seat belt retractor incorporating a seat belt force limiter to permit the restricted paying out of a safety belt with the absorption of energy, the force limiter having a first relatively high energy absorbing levels and a second relatively low energy absorbing level, there being a control mechanism operable to select the energy absorbing level in response to a crash related electric signal. The control mechanism being in the form of a mechanical arrangement, responsive to a relative movement between two components of the safety device caused by an initial belt force in excess of a predetermined force, the mechanical arrangement directly inhibiting the effective selection of the second relatively low energy absorbing levels by the control mechanism.
Preferably the control mechanism is operable to select the second relatively low energy absorbing level and the arrangement responsive to an initial belt force is operative to inhibit effective selection of the said second relatively low energy absorbing level. Because the mechanical arrangement directly inhibits the effective selection of the second low energy absorbing level, without the generation and processing of any electric control signals, a very fast acting operation may be achieved, and at a relatively low cost.
Preferably the retractor includes a two-part spindle within the retractor, a first part of the spindle being adapted to be locked, a second part of the spindle having the safety belt wound around it, the arrangement being such that the second part of the spindle may move relative to the first part when the initial belt force in excess of said predetermined force applied, the movement of the second part of the spindle relative to the fixed first part of the spindle actuating the arrangements which inhibits one of the energy levels.
Conveniently the second part of the spindle is connected to the first part of the spindle by means of an energy absorbing torsion bar, the energy absorbing torsion bar having two sections, a first section being operative to provide said first relatively high energy absorbing level and a second section being operative to provide said second relatively low energy absorbing level.
Preferably the control mechanism incorporates a locking element and an inhibiting element, the inhibiting element engaging part of the torsion bar between the first and the second section thereof, the locking element initially engaging part of the inhibiting element and the second part of the spindle to secure the inhibiting element to the second part of the spindle, the locking element being moveable to a release position in which the locking element does not secure the inhibiting element to the second part of the spindle.
Conveniently the locking element is a radially moveable locking element, the locking element initially being retained in an engaged position by means of a blocking element located adjacent one end of the locking element, the mechanism being configured to move the blocking element to a release position in response to the crash related electric signal.
Preferably the blocking element is in the form of a ring.
Advantageously the blocking element is moveable in response to the generation of gas by a pyrotechnic squib.
Alternatively the pyrotechnic squib is positioned to direct gas directly to the blocking member.
Conveniently there is a control element, the squib being positioned to direct gas to the control element to move the control element so that the movement of the control element moves the blocking element to the release position.
Advantageously the pyrotechnic squib is associated with at least one gas duct formed in the first part of the spindle and at least one gas duct in the second part of the spindle, the two gas ducts initially being co-aligned, so that a flow of gas may flow through both gas ducts to cause movement of the blocking element, the first part of the spindle being moveable relative to the second part of the spindle in response to the initial belt force in excess of a predetermined value, thus off-setting the gas flow ducts to prevent the flow of gas.
Preferably there are a plurality of the gas ducts in the first part of the spindle and a corresponding plurality of the gas flow ducts in the second part of the spindle.
Conveniently the blocking element is located adjacent a stop, the blocking element in one orientation being moveable past the stop, the blocking element, in any other orientation, not being moveable past the stop, the orientation of the blocking element being mounted to the second part of the spindle to be moveable with the second part of the spindle.
Advantageously the blocking element is in the form of a ring, the ring being provided with at least one inwardly directed finger, the finger being received within an axially extending groove formed in an outer region of the second part of the spindle.
Preferably the stop is formed on the first part of the spindle.
Conveniently two diametrically opposed stops are provided, each of a predetermined configuration, and the ring shaped blocking element is provided with two cut outs of corresponding shape and configuration.
Preferably wires are provided to supply the electric signal, a part of at least one wire extending from the first part of the spindle to the second part of the spindle, the part of the wire being configured to be broken on relative movement of the second part of the spindle relative to the first part.
Advantageously the inhibiting element is provided with a deformable portion which is configured to be deformed in response to relative movement of the second part of the spindle to a first part of the spindle, the deformable part being positioned to co-operate with a correspondingly configured part of the second part of the spindle, to engage the deformable part with the second part of the spindle so as to inhibit effective selection of said one of the energy levels.
Conveniently the deformable part is in the form of a deformable finger, the finger being deformed into a shaped recess provided within part of the second part of the spindle.